In the prior art, machines for particular use in handling formable, hardenable material such as concrete are known. For example, U.S. Pat. Nos. 3,606,827 and 3,749,505 disclose a self-propelled, self-steering, and self-leveling machine adapted to for handling, conveying, compacting and distributing formable material upon or along a work location. The formable material is distributed in a desired grade, slope, and directional configuration as defined by an external reference, such as a string line guide. The string line guide extends along a desired path of travel which is followed by the machine.
In one embodiment, the machine includes a material receiving hopper disposed on one of its lateral sides. A conveyor elevates the formable material from the receiving hopper and transfers the material to a compaction hopper disposed on the opposite of the machine. The material is thereafter passed by gravity feeding to a working tool, for example, a mule shoe.
A pair of drive units are utilized to provide desired movement of the machine. These are implemented as front and rear track-type crawler assemblies. To effectuate steering of the machine, a sensor arrangement is disposed to detect the directional position of the string line guide and to detect the elevation of the string line guide. For detecting the position of the string line guide, a pair of electrical steering sensors are utilized. Each includes a bar member pressed into engagement with the string line guide by a biasing spring. A first one of the sensors is associated with the forward moving device. The other sensor is associated with the rearward moving device. The machine automatically moves the traveling sensor perpendicular to the line of travel to provide integrated steering control of the front and rear crawler assemblies.
While such machines generally work for their intended purpose, the two-sensor system fails to allow the curb-forming machine to be automatically steered around tight radius turns or sharp curves. As a result, the machine requires a override for the steering system such that a user is required to maneuver the machine around tight radius turns or the like. However, some degree of precision is lost when the automatic control is disengaged in favor of manual control. That is, in most cases the machine can no longer fulfill the purpose for which it is intended, i.e., to form smooth curbs or the like. Accordingly, a need exists in the art for an improved curb-forming machine that overcomes this noted deficiency.